utils.cpp

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/*
    Copyright (C) 2003 - 2025
    by David White <dave@whitevine.net>
    Part of the Battle for Wesnoth Project https://www.wesnoth.org/
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY.
 
    See the COPYING file for more details.
*/
 
/**
 *  @file
 *  Support-routines for the SDL-graphics-library.
 */
 
#include "sdl/rect.hpp"
#include "sdl/utils.hpp"
#include "color.hpp"
#include "log.hpp"
#include "xBRZ/xbrz.hpp"
 
#include <algorithm>
#include <cassert>
#include <cstring>
#include "utils/ranges.hpp"
#include "utils/span.hpp"
 
#include <SDL2/SDL_version.h>
 
#include <boost/circular_buffer.hpp>
#include <boost/math/constants/constants.hpp>
 
static lg::log_domain log_display("display");
#define ERR_DP LOG_STREAM(err, log_display)
 
version_info sdl::get_version()
{
    SDL_version sdl_version;
    SDL_GetVersion(&sdl_version);
    return version_info(sdl_version.major, sdl_version.minor, sdl_version.patch);
}
 
bool sdl::runtime_at_least(uint8_t major, uint8_t minor, uint8_t patch)
{
    SDL_version ver;
    SDL_GetVersion(&ver);
    if(ver.major < major) return false;
    if(ver.major > major) return true;
    // major version equal
    if(ver.minor < minor) return false;
    if(ver.minor > minor) return true;
    // major and minor version equal
    if(ver.patch < patch) return false;
    return true;
}
 
surface scale_surface_xbrz(const surface & surf, std::size_t z)
{
    if(surf == nullptr)
        return nullptr;
 
    if (z > xbrz::SCALE_FACTOR_MAX) {
        PLAIN_LOG << "Cannot use xbrz scaling with zoom factor > " << xbrz::SCALE_FACTOR_MAX;
        z = 1;
    }
 
    if (z == 1) {
        surface temp = surf; // TODO: no temp surface
        return temp;
    }
 
    surface dst(surf->w *z, surf->h * z);
 
    if (z == 0) {
        PLAIN_LOG << "Create an empty image";
        return dst;
    }
 
    if(surf == nullptr || dst == nullptr) {
        PLAIN_LOG << "Could not create surface to scale onto";
        return nullptr;
    }
 
    {
        const_surface_lock src_lock(surf);
        surface_lock dst_lock(dst);
 
        xbrz::scale(z, src_lock.pixels(), dst_lock.pixels(), surf->w, surf->h, xbrz::ColorFormat::ARGB);
    }
 
    return dst;
}
 
// NOTE: Don't pass this function 0 scaling arguments.
surface scale_surface(const surface &surf, int w, int h)
{
    if(surf == nullptr)
        return nullptr;
 
    if(w == surf->w && h == surf->h) {
        return surf;
    }
    assert(w >= 0);
    assert(h >= 0);
 
    surface dst(w,h);
 
    if (w == 0 || h ==0) {
        PLAIN_LOG << "Create an empty image";
        return dst;
    }
 
    if(surf == nullptr || dst == nullptr) {
        PLAIN_LOG << "Could not create surface to scale onto";
        return nullptr;
    }
 
    {
        const_surface_lock src_lock(surf);
        surface_lock dst_lock(dst);
 
        const uint32_t* const src_pixels = src_lock.pixels();
        uint32_t* const dst_pixels = dst_lock.pixels();
 
        int32_t xratio = fixed_point_divide(surf->w,w);
        int32_t yratio = fixed_point_divide(surf->h,h);
 
        int32_t ysrc = 0;
        for(int ydst = 0; ydst != h; ++ydst, ysrc += yratio) {
            int32_t xsrc = 0;
            for(int xdst = 0; xdst != w; ++xdst, xsrc += xratio) {
                const int xsrcint = fixed_point_to_int(xsrc);
                const int ysrcint = fixed_point_to_int(ysrc);
 
                const uint32_t* const src_word = src_pixels + ysrcint*surf->w + xsrcint;
                uint32_t* const dst_word = dst_pixels +    ydst*dst->w + xdst;
                const int dx = (xsrcint + 1 < surf->w) ? 1 : 0;
                const int dy = (ysrcint + 1 < surf->h) ? surf->w : 0;
 
                uint8_t r,g,b,a;
                uint32_t rr,gg,bb,aa, temp;
 
                uint32_t pix[4], bilin[4];
 
                // This next part is the fixed point
                // equivalent of "take everything to
                // the right of the decimal point."
                // These fundamental weights decide
                // the contributions from various
                // input pixels. The labels assume
                // that the upper left corner of the
                // screen ("northeast") is 0,0 but the
                // code should still be consistent if
                // the graphics origin is actually
                // somewhere else.
                //
                // That is, the bilin array holds the
                // "geometric" weights. I.E. If I'm scaling
                // a 2 x 2 block a 10 x 10 block, then for
                // pixel (2,2) of output, the upper left
                // pixel should be 10:1 more influential than
                // the upper right, and also 10:1 more influential
                // than lower left, and 100:1 more influential
                // than lower right.
 
                const int32_t e = 0x000000FF & xsrc;
                const int32_t s = 0x000000FF & ysrc;
                const int32_t n = 0xFF - s;
                // Not called "w" to avoid hiding a function parameter
                // (would cause a compiler warning in MSVC2015 with /W4)
                const int32_t we = 0xFF - e;
 
                pix[0] = *src_word;              // northwest
                pix[1] = *(src_word + dx);       // northeast
                pix[2] = *(src_word + dy);       // southwest
                pix[3] = *(src_word + dx + dy);  // southeast
 
                bilin[0] = n*we;
                bilin[1] = n*e;
                bilin[2] = s*we;
                bilin[3] = s*e;
 
                int loc;
                rr = bb = gg = aa = 0;
                for (loc=0; loc<4; loc++) {
                  a = pix[loc] >> 24;
                  r = pix[loc] >> 16;
                  g = pix[loc] >> 8;
                  b = pix[loc] >> 0;
 
                  //We also have to implement weighting by alpha for the RGB components
                  //If a unit has some parts solid and some parts translucent,
                  //i.e. a red cloak but a dark shadow, then when we scale in
                  //the shadow shouldn't appear to become red at the edges.
                  //This part also smoothly interpolates between alpha=0 being
                  //transparent and having no contribution, vs being opaque.
                  temp = (a * bilin[loc]);
                  rr += r * temp;
                  gg += g * temp;
                  bb += b * temp;
                  aa += temp;
                }
 
                a = aa >> (16); // we average the alphas, they don't get weighted by any other factor besides bilin
                if (a != 0) {
                    rr /= a;    // finish alpha weighting: divide by sum of alphas
                    gg /= a;
                    bb /= a;
                }
                r = rr >> (16); // now shift over by 16 for the bilin part
                g = gg >> (16);
                b = bb >> (16);
                *dst_word = (a << 24) + (r << 16) + (g << 8) + b;
            }
        }
    }
 
    return dst;
}
 
surface scale_surface_legacy(const surface &surf, int w, int h)
{
    if(surf == nullptr)
        return nullptr;
 
    if(w == surf->w && h == surf->h) {
        return surf;
    }
    assert(w >= 0);
    assert(h >= 0);
 
    surface dst(w,h);
 
    if(surf == nullptr || dst == nullptr) {
        PLAIN_LOG << "Could not create surface to scale onto";
        return nullptr;
    }
 
    {
        const_surface_lock src_lock(surf);
        surface_lock dst_lock(dst);
 
        const uint32_t* const src_pixels = src_lock.pixels();
        uint32_t* const dst_pixels = dst_lock.pixels();
 
        int32_t xratio = fixed_point_divide(surf->w,w);
        int32_t yratio = fixed_point_divide(surf->h,h);
 
        int32_t ysrc = 0;
        for(int ydst = 0; ydst != h; ++ydst, ysrc += yratio) {
            int32_t xsrc = 0;
            for(int xdst = 0; xdst != w; ++xdst, xsrc += xratio) {
                const int xsrcint = fixed_point_to_int(xsrc);
                const int ysrcint = fixed_point_to_int(ysrc);
 
                const uint32_t* const src_word = src_pixels + ysrcint*surf->w + xsrcint;
                uint32_t* const dst_word = dst_pixels +    ydst*dst->w + xdst;
                const int dx = (xsrcint + 1 < surf->w) ? 1 : 0;
                const int dy = (ysrcint + 1 < surf->h) ? surf->w : 0;
 
                uint8_t r,g,b,a;
                uint32_t rr,gg,bb,aa;
                uint16_t avg_r, avg_g, avg_b;
                uint32_t pix[4], bilin[4];
 
                // This next part is the fixed point
                // equivalent of "take everything to
                // the right of the decimal point."
                // These fundamental weights decide
                // the contributions from various
                // input pixels. The labels assume
                // that the upper left corner of the
                // screen ("northeast") is 0,0 but the
                // code should still be consistent if
                // the graphics origin is actually
                // somewhere else.
 
                const int32_t east = 0x000000FF & xsrc;
                const int32_t south = 0x000000FF & ysrc;
                const int32_t north = 0xFF - south;
                const int32_t west = 0xFF - east;
 
                pix[0] = *src_word;              // northwest
                pix[1] = *(src_word + dx);       // northeast
                pix[2] = *(src_word + dy);       // southwest
                pix[3] = *(src_word + dx + dy);  // southeast
 
                bilin[0] = north*west;
                bilin[1] = north*east;
                bilin[2] = south*west;
                bilin[3] = south*east;
 
                // Scope out the neighboorhood, see
                // what the pixel values are like.
 
                int count = 0;
                avg_r = avg_g = avg_b = 0;
                int loc;
                for (loc=0; loc<4; loc++) {
                  a = pix[loc] >> 24;
                  r = pix[loc] >> 16;
                  g = pix[loc] >> 8;
                  b = pix[loc] >> 0;
                  if (a != 0) {
                    avg_r += r;
                    avg_g += g;
                    avg_b += b;
                    count++;
                  }
                }
                if (count>0) {
                  avg_r /= count;
                  avg_b /= count;
                  avg_g /= count;
                }
 
                // Perform modified bilinear interpolation.
                // Don't trust any color information from
                // an RGBA sample when the alpha channel
                // is set to fully transparent.
                //
                // Some of the input images are hex tiles,
                // created using a hexagon shaped alpha channel
                // that is either set to full-on or full-off.
 
                rr = gg = bb = aa = 0;
                for (loc=0; loc<4; loc++) {
                  a = pix[loc] >> 24;
                  r = pix[loc] >> 16;
                  g = pix[loc] >> 8;
                  b = pix[loc] >> 0;
                  if (a == 0) {
                    r = static_cast<uint8_t>(avg_r);
                    g = static_cast<uint8_t>(avg_g);
                    b = static_cast<uint8_t>(avg_b);
                  }
                  rr += r * bilin[loc];
                  gg += g * bilin[loc];
                  bb += b * bilin[loc];
                  aa += a * bilin[loc];
                }
                r = rr >> 16;
                g = gg >> 16;
                b = bb >> 16;
                a = aa >> 16;
                *dst_word = (a << 24) + (r << 16) + (g << 8) + b;
            }
        }
    }
 
    return dst;
}
 
surface scale_surface_sharp(const surface& surf, int w, int h)
{
    if(surf == nullptr) {
        return nullptr;
    }
    if(w == surf->w && h == surf->h) {
        return surf;
    }
 
    assert(w >= 0);
    assert(h >= 0);
    surface dst(w, h);
    if(dst == nullptr) {
        PLAIN_LOG << "Could not create surface to scale onto";
        return nullptr;
    }
 
    if(w == 0 || h == 0) {
        PLAIN_LOG << "Creating an empty image";
        return dst;
    }
 
    {
        const_surface_lock src_lock(surf);
        surface_lock dst_lock(dst);
 
        const uint32_t* const src_pixels = src_lock.pixels();
        uint32_t* const dst_pixels = dst_lock.pixels();
 
        const int src_w = surf->w;
        const int src_h = surf->h;
 
        const float xratio = static_cast<float>(src_w) / static_cast<float>(w);
        const float yratio = static_cast<float>(src_h) / static_cast<float>(h);
        for(int ydst = 0; ydst != h; ++ydst) {
            for(int xdst = 0; xdst != w; ++xdst) {
                // Project dst pixel to a single corresponding src pixel by scale and simply take it
                const int xsrc = std::floor(static_cast<float>(xdst) * xratio);
                const int ysrc = std::floor(static_cast<float>(ydst) * yratio);
                dst_pixels[ydst * dst->w + xdst] = src_pixels[ysrc * src_w + xsrc];
            }
        }
    }
 
    return dst;
}
 
void adjust_surface_color(surface& nsurf, int red, int green, int blue)
{
    if(nsurf && (red != 0 || green != 0 || blue != 0)) {
        surface_lock lock(nsurf);
 
        for(auto& pixel : lock.pixel_span()) {
            auto [r, g, b, alpha] = color_t::from_argb_bytes(pixel);
 
            r = std::clamp(static_cast<int>(r) + red, 0, 255);
            g = std::clamp(static_cast<int>(g) + green, 0, 255);
            b = std::clamp(static_cast<int>(b) + blue, 0, 255);
 
            pixel = (alpha << 24) + (r << 16) + (g << 8) + b;
        }
    }
}
 
void greyscale_image(surface& nsurf)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        for(auto& pixel : lock.pixel_span()) {
            auto [r, g, b, alpha] = color_t::from_argb_bytes(pixel);
 
            // Use the correct formula for RGB to grayscale conversion.
            // Ok, this is no big deal :)
            // The correct formula being:
            // gray=0.299red+0.587green+0.114blue
            const uint8_t avg = static_cast<uint8_t>((
                77  * static_cast<uint16_t>(r) +
                150 * static_cast<uint16_t>(g) +
                29  * static_cast<uint16_t>(b)  ) / 256);
 
            pixel = (alpha << 24) | (avg << 16) | (avg << 8) | avg;
        }
    }
}
 
void monochrome_image(surface& nsurf, const int threshold)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        for(auto& pixel : lock.pixel_span()) {
            auto [r, g, b, alpha] = color_t::from_argb_bytes(pixel);
 
            // first convert the pixel to grayscale
            // if the resulting value is above the threshold make it black
            // else make it white
            uint8_t result = static_cast<uint8_t>(0.299 * r + 0.587 * g + 0.114 * b) > threshold ? 255 : 0;
 
            pixel = (alpha << 24) | (result << 16) | (result << 8) | result;
        }
    }
}
 
void sepia_image(surface& nsurf)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        for(auto& pixel : lock.pixel_span()) {
            auto [r, g, b, alpha] = color_t::from_argb_bytes(pixel);
 
            // this is the formula for applying a sepia effect
            // that can be found on various web sites
            uint8_t outR = std::min(255, static_cast<int>((r * 0.393) + (g * 0.769) + (b * 0.189)));
            uint8_t outG = std::min(255, static_cast<int>((r * 0.349) + (g * 0.686) + (b * 0.168)));
            uint8_t outB = std::min(255, static_cast<int>((r * 0.272) + (g * 0.534) + (b * 0.131)));
 
            pixel = (alpha << 24) | (outR << 16) | (outG << 8) | (outB);
        }
    }
}
 
void negative_image(surface& nsurf, const int thresholdR, const int thresholdG, const int thresholdB)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        for(auto& pixel : lock.pixel_span()) {
            auto [r, g, b, alpha] = color_t::from_argb_bytes(pixel);
 
            // invert he channel only if its value is greater than the supplied threshold
            // this can be used for solarization effects
            // for a full negative effect, use a value of -1
            // 255 is a no-op value (doesn't do anything, since a uint8_t cannot contain a greater value than that)
            uint8_t newR = r > thresholdR ? 255 - r : r;
            uint8_t newG = g > thresholdG ? 255 - g : g;
            uint8_t newB = b > thresholdB ? 255 - b : b;
 
            pixel = (alpha << 24) | (newR << 16) | (newG << 8) | (newB);
        }
    }
}
 
void alpha_to_greyscale(surface& nsurf)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        for(auto& pixel : lock.pixel_span()) {
            uint8_t alpha = pixel >> 24;
 
            pixel = (0xff << 24) | (alpha << 16) | (alpha << 8) | alpha;
        }
    }
}
 
void wipe_alpha(surface& nsurf)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        for(auto& pixel : lock.pixel_span()) {
            pixel = 0xff000000 | pixel;
        }
    }
}
 
 
void shadow_image(surface& surf, int scale)
{
    if(surf == nullptr)
        return;
 
    // we blur it, and reuse the neutral surface created by the blur function
    blur_alpha_surface(surf, 2*scale);
 
    {
        surface_lock lock(surf);
 
        for(auto& pixel : lock.pixel_span()) {
            uint8_t alpha = pixel >> 24;
 
            // increase alpha and color in black (RGB=0)
            // with some stupid optimization for handling maximum values
            if(alpha < 255 / 4) {
                pixel = (alpha * 4) << 24;
            } else {
                pixel = 0xFF000000; // we hit the maximum
            }
        }
    }
}
 
void swap_channels_image(surface& nsurf, channel r, channel g, channel b, channel a)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        for(auto& pixel : lock.pixel_span()) {
            auto [red, green, blue, alpha] = color_t::from_argb_bytes(pixel);
            uint8_t newRed, newGreen, newBlue, newAlpha;
 
            switch (r) {
                case RED:
                    newRed = red;
                    break;
                case GREEN:
                    newRed = green;
                    break;
                case BLUE:
                    newRed = blue;
                    break;
                case ALPHA:
                    newRed = alpha;
                    break;
                default:
                    return;
            }
 
            switch (g) {
                case RED:
                    newGreen = red;
                    break;
                case GREEN:
                    newGreen = green;
                    break;
                case BLUE:
                    newGreen = blue;
                    break;
                case ALPHA:
                    newGreen = alpha;
                    break;
                default:
                    return;
            }
 
            switch (b) {
                case RED:
                    newBlue = red;
                    break;
                case GREEN:
                    newBlue = green;
                    break;
                case BLUE:
                    newBlue = blue;
                    break;
                case ALPHA:
                    newBlue = alpha;
                    break;
                default:
                    return;
            }
 
            switch (a) {
                case RED:
                    newAlpha = red;
                    break;
                case GREEN:
                    newAlpha = green;
                    break;
                case BLUE:
                    newAlpha = blue;
                    break;
                case ALPHA:
                    newAlpha = alpha;
                    break;
                default:
                    return;
            }
 
            pixel = (newAlpha << 24) | (newRed << 16) | (newGreen << 8) | newBlue;
        }
    }
}
 
void recolor_image(surface& nsurf, const color_mapping& map_rgb)
{
    if(nsurf == nullptr)
        return;
 
    if(map_rgb.empty()) {
        return;
    }
 
    surface_lock lock(nsurf);
 
    for(auto& pixel : lock.pixel_span()) {
        auto color = color_t::from_argb_bytes(pixel);
 
        // Palette uses only RGB channels, so remove alpha
        uint8_t old_alpha = color.a;
        color.a = ALPHA_OPAQUE;
 
        auto iter = map_rgb.find(color);
        if(iter == map_rgb.end()) {
            continue;
        }
 
        // Set new color, restore alpha
        color = iter->second;
        color.a = old_alpha;
 
        pixel = color.to_argb_bytes();
    }
}
 
void brighten_image(surface& nsurf, int32_t amount)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        if (amount < 0) amount = 0;
        for(auto& pixel : lock.pixel_span()) {
            auto [r, g, b, alpha] = color_t::from_argb_bytes(pixel);
 
            r = std::min<unsigned>(fixed_point_multiply(r, amount), 255);
            g = std::min<unsigned>(fixed_point_multiply(g, amount), 255);
            b = std::min<unsigned>(fixed_point_multiply(b, amount), 255);
 
            pixel = (alpha << 24) + (r << 16) + (g << 8) + b;
        }
    }
}
 
void adjust_surface_alpha(surface& surf, uint8_t alpha_mod)
{
    if(surf == nullptr) {
        return;
    }
 
    SDL_SetSurfaceAlphaMod(surf, alpha_mod);
}
 
void adjust_surface_alpha_add(surface& nsurf, int amount)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        for(auto& pixel : lock.pixel_span()) {
            auto [r, g, b, alpha] = color_t::from_argb_bytes(pixel);
 
            alpha = uint8_t(std::clamp(static_cast<int>(alpha) + amount, 0, 255));
            pixel = (alpha << 24) + (r << 16) + (g << 8) + b;
        }
    }
}
 
bool mask_surface(surface& nsurf, const surface& nmask, const std::string& filename)
{
    if(nsurf == nullptr) {
        return true;
    }
    if(nmask == nullptr) {
        return false;
    }
 
    if (nsurf->w != nmask->w) {
        // we don't support efficiently different width.
        // (different height is not a real problem)
        // This function is used on all hexes and usually only for that
        // so better keep it simple and efficient for the normal case
        std::stringstream ss;
        ss << "Detected an image with bad dimensions: ";
        if(!filename.empty()) ss << filename << ": ";
        ss << nsurf->w << "x" << nsurf->h;
        PLAIN_LOG << ss.str();
        PLAIN_LOG << "It will not be masked, please use: "<< nmask->w << "x" << nmask->h;
        return false;
    }
 
    uint32_t cumulative_alpha{0};
    {
        surface_lock lock(nsurf);
        const_surface_lock mlock(nmask);
 
        utils::span surf_pixels = lock.pixel_span();
        utils::span mask_pixels = mlock.pixel_span();
 
        // Note: any pixels outside the range of the smaller surface are ignored.
        const auto sentinel = std::min(surf_pixels.size(), mask_pixels.size());
 
        for(std::size_t i = 0; i < sentinel; ++i) {
            const uint32_t surf_alpha = surf_pixels[i] & SDL_ALPHA_MASK;
            const uint32_t mask_alpha = mask_pixels[i] & SDL_ALPHA_MASK;
 
            const auto min_alpha = std::min(surf_alpha, mask_alpha);
 
            // Clear the alpha bits before writing the new alpha value.
            surf_pixels[i] &= ~SDL_ALPHA_MASK;
            surf_pixels[i] |= min_alpha;
 
            // This will quickly saturate the leftmost 8 bits,
            // but we only care whether the final result is 0.
            cumulative_alpha |= min_alpha;
        }
    }
 
    return cumulative_alpha == 0;
}
 
bool in_mask_surface(const surface& nsurf, const surface& nmask)
{
    if(nsurf == nullptr) {
        return false;
    }
    if(nmask == nullptr){
        return true;
    }
 
    if (nsurf->w != nmask->w || nsurf->h != nmask->h ) {
        // not same size, consider it doesn't fit
        return false;
    }
 
    const_surface_lock lock(nsurf);
    const_surface_lock mlock(nmask);
 
    utils::span surf_pixels = lock.pixel_span();
    utils::span mask_pixels = mlock.pixel_span();
 
    // Note: unlike in mask_surface, both ranges here have the same size.
    for(std::size_t i = 0; i < surf_pixels.size(); ++i) {
        const uint32_t surf_alpha = surf_pixels[i] & SDL_ALPHA_MASK;
        const uint32_t mask_alpha = mask_pixels[i] & SDL_ALPHA_MASK;
 
        // A visible pixel (non-zero alpha) which the mask would otherwise hide.
        if(surf_alpha && mask_alpha == 0) {
            return false;
        }
    }
 
    return true;
}
 
void light_surface(surface& nsurf, const surface &lightmap)
{
    if(nsurf == nullptr) {
        return;
    }
    if(lightmap == nullptr) {
        return;
    }
 
    if (nsurf->w != lightmap->w) {
        // we don't support efficiently different width.
        // (different height is not a real problem)
        // This function is used on all hexes and usually only for that
        // so better keep it simple and efficient for the normal case
        PLAIN_LOG << "Detected an image with bad dimensions: " << nsurf->w << "x" << nsurf->h;
        PLAIN_LOG << "It will not be lighted, please use: "<< lightmap->w << "x" << lightmap->h;
        return;
    }
    {
        surface_lock lock(nsurf);
        const_surface_lock llock(lightmap);
 
        uint32_t* beg = lock.pixels();
        uint32_t* end = beg + nsurf.area();
        const uint32_t* lbeg = llock.pixels();
        const uint32_t* lend = lbeg + lightmap.area();
 
        while(beg != end && lbeg != lend) {
            auto [lr, lg, lb, la] = color_t::from_argb_bytes(*lbeg);
            auto [r, g, b, alpha] = color_t::from_argb_bytes(*beg);
 
            int dr = (static_cast<int>(lr) - 128) * 2;
            int dg = (static_cast<int>(lg) - 128) * 2;
            int db = (static_cast<int>(lb) - 128) * 2;
 
            //note that r + dr will promote r to int (needed to avoid uint8_t math)
            r = std::clamp(r + dr, 0, 255);
            g = std::clamp(g + dg, 0, 255);
            b = std::clamp(b + db, 0, 255);
 
            *beg = (alpha << 24) + (r << 16) + (g << 8) + b;
 
            ++beg;
            ++lbeg;
        }
    }
}
 
void blur_surface(surface& surf, rect rect, int depth)
{
    if(surf == nullptr) {
        return;
    }
 
    const int max_blur = 256;
    if(depth > max_blur) {
        depth = max_blur;
    }
 
    uint32_t queue[max_blur];
    const uint32_t* end_queue = queue + max_blur;
 
    const uint32_t ff = 0xff;
 
    const unsigned pixel_offset = rect.y * surf->w + rect.x;
 
    surface_lock lock(surf);
    for(int y = 0; y < rect.h; ++y) {
        const uint32_t* front = &queue[0];
        uint32_t* back = &queue[0];
        uint32_t red = 0, green = 0, blue = 0, avg = 0;
        uint32_t* p = lock.pixels() + pixel_offset + y * surf->w;
        for(int x = 0; x <= depth && x < rect.w; ++x, ++p) {
            red += ((*p) >> 16)&0xFF;
            green += ((*p) >> 8)&0xFF;
            blue += (*p)&0xFF;
            ++avg;
            *back++ = *p;
            if(back == end_queue) {
                back = &queue[0];
            }
        }
 
        p = lock.pixels() + pixel_offset + y * surf->w;
        for(int x = 0; x < rect.w; ++x, ++p) {
            *p = 0xFF000000
                    | (std::min(red/avg,ff) << 16)
                    | (std::min(green/avg,ff) << 8)
                    | std::min(blue/avg,ff);
 
            if(x >= depth) {
                red -= ((*front) >> 16)&0xFF;
                green -= ((*front) >> 8)&0xFF;
                blue -= *front&0xFF;
                --avg;
                ++front;
                if(front == end_queue) {
                    front = &queue[0];
                }
            }
 
            if(x + depth+1 < rect.w) {
                uint32_t* q = p + depth+1;
                red += ((*q) >> 16)&0xFF;
                green += ((*q) >> 8)&0xFF;
                blue += (*q)&0xFF;
                ++avg;
                *back++ = *q;
                if(back == end_queue) {
                    back = &queue[0];
                }
            }
        }
    }
 
    for(int x = 0; x < rect.w; ++x) {
        const uint32_t* front = &queue[0];
        uint32_t* back = &queue[0];
        uint32_t red = 0, green = 0, blue = 0, avg = 0;
        uint32_t* p = lock.pixels() + pixel_offset + x;
        for(int y = 0; y <= depth && y < rect.h; ++y, p += surf->w) {
            red += ((*p) >> 16)&0xFF;
            green += ((*p) >> 8)&0xFF;
            blue += *p&0xFF;
            ++avg;
            *back++ = *p;
            if(back == end_queue) {
                back = &queue[0];
            }
        }
 
        p = lock.pixels() + pixel_offset + x;
        for(int y = 0; y < rect.h; ++y, p += surf->w) {
            *p = 0xFF000000
                    | (std::min(red/avg,ff) << 16)
                    | (std::min(green/avg,ff) << 8)
                    | std::min(blue/avg,ff);
 
            if(y >= depth) {
                red -= ((*front) >> 16)&0xFF;
                green -= ((*front) >> 8)&0xFF;
                blue -= *front&0xFF;
                --avg;
                ++front;
                if(front == end_queue) {
                    front = &queue[0];
                }
            }
 
            if(y + depth+1 < rect.h) {
                uint32_t* q = p + (depth+1)*surf->w;
                red += ((*q) >> 16)&0xFF;
                green += ((*q) >> 8)&0xFF;
                blue += (*q)&0xFF;
                ++avg;
                *back++ = *q;
                if(back == end_queue) {
                    back = &queue[0];
                }
            }
        }
    }
}
 
void blur_alpha_surface(surface& res, int depth)
{
    if(res == nullptr) {
        return;
    }
 
    const int max_blur = 256;
    if(depth > max_blur) {
        depth = max_blur;
    }
 
    struct Pixel{
        uint8_t alpha;
        uint8_t red;
        uint8_t green;
        uint8_t blue;
        Pixel(uint32_t* p)
          : alpha(((*p) >> 24)&0xFF)
          , red(((*p) >> 16)&0xFF)
          , green(((*p) >> 8)&0xFF)
          , blue((*p)&0xFF) {}
    };
    struct Average{
        uint32_t alpha;
        uint32_t red;
        uint32_t green;
        uint32_t blue;
        Average() : alpha(), red(), green(), blue()
        {}
        Average& operator+=(const Pixel& pix){
            red   += pix.alpha * pix.red;
            green += pix.alpha * pix.green;
            blue  += pix.alpha * pix.blue;
            alpha += pix.alpha;
            return *this;
        }
        Average& operator-=(const Pixel& pix){
            red   -= pix.alpha * pix.red;
            green -= pix.alpha * pix.green;
            blue  -= pix.alpha * pix.blue;
            alpha -= pix.alpha;
            return *this;
        }
        uint32_t operator()(unsigned num){
            const uint32_t ff = 0xff;
            if(!alpha){
                return 0;
            }
            return (std::min(alpha/num,ff) << 24)
                | (std::min(red/alpha,ff) << 16)
                | (std::min(green/alpha,ff) << 8)
                | std::min(blue/alpha,ff);
        }
    };
 
    boost::circular_buffer<Pixel> queue(depth*2+1);
 
    surface_lock lock(res);
    int x, y;
    // Iterate over rows, blurring each row horizontally
    for(y = 0; y < res->h; ++y) {
        // Sum of pixel values stored here
        Average avg;
 
        // Preload the first depth+1 pixels
        uint32_t* p = lock.pixels() + y*res->w;
        for(x = 0; x <= depth && x < res->w; ++x, ++p) {
            assert(!queue.full());
            queue.push_back(Pixel{p});
            avg += queue.back();
        }
 
        // This is the actual inner loop
        p = lock.pixels() + y*res->w;
        for(x = 0; x < res->w; ++x, ++p) {
            // Write the current average
            const uint32_t num = queue.size();
            *p = avg(num);
 
            // Unload earlier pixels that are now too far away
            if(x >= depth) {
                avg -= queue.front();
                assert(!queue.empty());
                queue.pop_front();
            }
 
            // Add new pixels
            if(x + depth+1 < res->w) {
                uint32_t* q = p + depth+1;
                assert(!queue.full());
                queue.push_back(Pixel{q});
                avg += queue.back();
            }
        }
        assert(static_cast<int>(queue.size()) == std::min(depth, res->w));
        queue.clear();
    }
 
    // Iterate over columns, blurring each column vertically
    for(x = 0; x < res->w; ++x) {
        // Sum of pixel values stored here
        Average avg;
 
        // Preload the first depth+1 pixels
        uint32_t* p = lock.pixels() + x;
        for(y = 0; y <= depth && y < res->h; ++y, p += res->w) {
            assert(!queue.full());
            queue.push_back(Pixel{p});
            avg += queue.back();
        }
 
        // This is the actual inner loop
        p = lock.pixels() + x;
        for(y = 0; y < res->h; ++y, p += res->w) {
            // Write the current average
            const uint32_t num = queue.size();
            *p = avg(num);
 
            // Unload earlier pixels that are now too far away
            if(y >= depth) {
                avg -= queue.front();
                assert(!queue.empty());
                queue.pop_front();
            }
 
            // Add new pixels
            if(y + depth+1 < res->h) {
                uint32_t* q = p + (depth+1)*res->w;
                assert(!queue.full());
                queue.push_back(Pixel{q});
                avg += queue.back();
            }
        }
        assert(static_cast<int>(queue.size()) == std::min(depth, res->h));
        queue.clear();
    }
}
 
surface cut_surface(const surface &surf, const rect& r)
{
    if(surf == nullptr)
        return nullptr;
 
    surface res(r.w, r.h);
 
    if(res == nullptr) {
        PLAIN_LOG << "Could not create a new surface in cut_surface()";
        return nullptr;
    }
 
    std::size_t sbpp = surf->format->BytesPerPixel;
    std::size_t spitch = surf->pitch;
    std::size_t rbpp = res->format->BytesPerPixel;
    std::size_t rpitch = res->pitch;
 
    // compute the areas to copy
    rect src_rect = r;
    rect dst_rect { 0, 0, r.w, r.h };
 
    if (src_rect.x < 0) {
        if (src_rect.x + src_rect.w <= 0)
            return res;
        dst_rect.x -= src_rect.x;
        dst_rect.w += src_rect.x;
        src_rect.w += src_rect.x;
        src_rect.x = 0;
    }
    if (src_rect.y < 0) {
        if (src_rect.y + src_rect.h <= 0)
            return res;
        dst_rect.y -= src_rect.y;
        dst_rect.h += src_rect.y;
        src_rect.h += src_rect.y;
        src_rect.y = 0;
    }
 
    if(src_rect.x >= surf->w || src_rect.y >= surf->h)
        return res;
 
    const_surface_lock slock(surf);
    surface_lock rlock(res);
 
    const uint8_t* src = reinterpret_cast<const uint8_t *>(slock.pixels());
    uint8_t* dest = reinterpret_cast<uint8_t *>(rlock.pixels());
 
    for(int y = 0; y < src_rect.h && (src_rect.y + y) < surf->h; ++y) {
        const uint8_t* line_src  = src  + (src_rect.y + y) * spitch + src_rect.x * sbpp;
        uint8_t* line_dest = dest + (dst_rect.y + y) * rpitch + dst_rect.x * rbpp;
        std::size_t size = src_rect.w + src_rect.x <= surf->w ? src_rect.w : surf->w - src_rect.x;
 
        assert(rpitch >= src_rect.w * rbpp);
        memcpy(line_dest, line_src, size * rbpp);
    }
 
    return res;
}
 
void blend_surface(surface& nsurf, const double amount, const color_t color)
{
    if(nsurf) {
        surface_lock lock(nsurf);
 
        uint16_t ratio = amount * 256;
        const uint16_t red   = ratio * color.r;
        const uint16_t green = ratio * color.g;
        const uint16_t blue  = ratio * color.b;
        ratio = 256 - ratio;
 
        for(auto& pixel : lock.pixel_span()) {
            auto [r, g, b, a] = color_t::from_argb_bytes(pixel);
 
            r = (ratio * r + red)   >> 8;
            g = (ratio * g + green) >> 8;
            b = (ratio * b + blue)  >> 8;
 
            pixel = (a << 24) | (r << 16) | (g << 8) | b;
        }
    }
}
 
/* Simplified RotSprite algorithm.
 * http://en.wikipedia.org/wiki/Image_scaling#RotSprite
 * Lifted from: http://github.com/salmonmoose/SpriteRotator
 * 1) Zoom the source image by a certain factor.
 * 2) Scan the zoomed source image at every step=offset and put it in the result. */
surface rotate_any_surface(const surface& surf, float angle, int zoom, int offset)
{
    int src_w, src_h, dst_w, dst_h;
    float min_x, min_y, sine, cosine;
    {
        float max_x, max_y;
        // convert angle to radiant (angle * 2 * PI) / 360
        const float radians = angle * boost::math::constants::pi<float>() / 180;
        cosine = std::cos(radians);
        sine   = std::sin(radians);
        // calculate the size of the dst image
        src_w = surf->w * zoom;
        src_h = surf->h * zoom;
        /* See http://en.wikipedia.org/wiki/Rotation_(mathematics) */
        const float point_1x = src_h * -sine;
        const float point_1y = src_h * cosine;
        const float point_2x = src_w * cosine - src_h * sine;
        const float point_2y = src_h * cosine + src_w * sine;
        const float point_3x = src_w * cosine;
        const float point_3y = src_w * sine;
        /* After the rotation, the new image has different dimensions.
         * E.g.: The maximum height equals the former diagonal in case the angle is 45, 135, 225 or 315 degree.
         * See http://en.wikipedia.org/wiki/File:Rotation_illustration2.svg to get the idea. */
        min_x = std::min(0.0F, std::min(point_1x, std::min(point_2x, point_3x)));
        min_y = std::min(0.0F, std::min(point_1y, std::min(point_2y, point_3y)));
        max_x = (angle >  90 && angle < 180) ? 0 : std::max(point_1x, std::max(point_2x, point_3x));
        max_y = (angle > 180 && angle < 270) ? 0 : std::max(point_1y, std::max(point_2y, point_3y));
        dst_w = static_cast<int>(ceil(std::abs(max_x) - min_x)) / zoom;
        dst_h = static_cast<int>(ceil(std::abs(max_y) - min_y)) / zoom;
    }
    surface dst(dst_w, dst_h);
    {
        surface_lock dst_lock(dst);
        uint32_t* const dst_pixels = dst_lock.pixels();
 
        const surface src = scale_surface(surf, src_w, src_h);
        const_surface_lock src_lock(src);
        const uint32_t* const src_pixels = src_lock.pixels();
 
        const float scale =   1.f / zoom;
        const int   max_x = dst_w * zoom;
        const int   max_y = dst_h * zoom;
        /* Loop through the zoomed src image,
         * take every pixel in steps with offset distance and place it in the dst image. */
        for (int x = 0; x < max_x; x += offset)
            for (int y = 0; y < max_y; y += offset) {
                // calculate the src pixel that fits in the dst
                const float source_x = (x + min_x)*cosine + (y + min_y)*sine;
                const float source_y = (y + min_y)*cosine - (x + min_x)*sine;
                // if the pixel exists on the src surface
                if (source_x >= 0 && source_x < src_w && source_y >= 0 && source_y < src_h) {
                    // get it from the src surface and place it on the dst surface
                    dst_pixels[int((y * scale)) * dst->w + int((x * scale))] =
                        src_pixels[int(source_y) * src->w + int(source_x)];
                }
            }
    }
 
    return dst;
}
 
// Rotates a surface 180 degrees.
surface rotate_180_surface(const surface& surf)
{
    if ( surf == nullptr )
        return nullptr;
 
    surface nsurf = surf.clone();
 
    if ( nsurf == nullptr ) {
        PLAIN_LOG << "could not make neutral surface...";
        return nullptr;
    }
 
    {// Code block to limit the scope of the surface lock.
        surface_lock lock(nsurf);
        uint32_t* const pixels = lock.pixels();
 
        // Swap pixels in the upper half of the image with
        // those in the lower half.
        for (int y=0; y != nsurf->h/2; ++y) {
            for(int x=0; x != nsurf->w; ++x) {
                const int index1 = y*nsurf->w + x;
                const int index2 = (nsurf->h-y)*nsurf->w - x - 1;
                std::swap(pixels[index1],pixels[index2]);
            }
        }
 
        if ( is_odd(nsurf->h) ) {
            // The middle row still needs to be processed.
            for (int x=0; x != nsurf->w/2; ++x) {
                const int index1 = (nsurf->h/2)*nsurf->w + x;
                const int index2 = (nsurf->h/2)*nsurf->w + (nsurf->w - x - 1);
                std::swap(pixels[index1],pixels[index2]);
            }
        }
    }
 
    return nsurf;
}
 
// Rotates a surface 90 degrees, either clockwise or counter-clockwise.
surface rotate_90_surface(const surface& surf, bool clockwise)
{
    if(surf == nullptr)
        return surf;
 
    surface dst(surf->h, surf->w); // Flipped dimensions.
 
    if ( surf == nullptr  ||  dst == nullptr ) {
        PLAIN_LOG << "could not make neutral surface...";
        return nullptr;
    }
 
    {
        const_surface_lock src_lock(surf);
        surface_lock dst_lock(dst);
 
        const uint32_t* const src_pixels = src_lock.pixels();
        uint32_t* const dst_pixels = dst_lock.pixels();
 
        // Copy the pixels.
        for(int y = 0; y != surf->h; ++y) {
            for ( int x = 0; x != surf->w; ++x ) {
                const int src_index = y*surf->w + x;
                const int dst_index = clockwise ?
                                          x*dst->w + (dst->w-1-y) :
                                          (dst->h-1-x)*dst->w + y;
                dst_pixels[dst_index] = src_pixels[src_index];
            }
        }
    }
 
    return dst;
}
 
void flip_surface(surface& nsurf)
{
    if(nsurf) {
        surface_lock lock(nsurf);
        uint32_t* const pixels = lock.pixels();
 
        for(int y = 0; y != nsurf->h; ++y) {
            for(int x = 0; x != nsurf->w/2; ++x) {
                const int index1 = y*nsurf->w + x;
                const int index2 = (y+1)*nsurf->w - x - 1;
                std::swap(pixels[index1],pixels[index2]);
            }
        }
    }
}
 
void flop_surface(surface& nsurf)
{
    if(nsurf) {
        surface_lock lock(nsurf);
        uint32_t* const pixels = lock.pixels();
 
        for(int x = 0; x != nsurf->w; ++x) {
            for(int y = 0; y != nsurf->h/2; ++y) {
                const int index1 = y*nsurf->w + x;
                const int index2 = (nsurf->h-y-1)*nsurf->w + x;
                std::swap(pixels[index1],pixels[index2]);
            }
        }
    }
}
 
surface get_surface_portion(const surface &src, rect &area)
{
    if (src == nullptr) {
        return nullptr;
    }
 
    // Check if there is something in the portion
    if(area.x >= src->w || area.y >= src->h || area.x + area.w < 0 || area.y + area.h < 0) {
        return nullptr;
    }
 
    if(area.x + area.w > src->w) {
        area.w = src->w - area.x;
    }
    if(area.y + area.h > src->h) {
        area.h = src->h - area.y;
    }
 
    // use same format as the source (almost always the screen)
    surface dst(area.w, area.h);
 
    if(dst == nullptr) {
        PLAIN_LOG << "Could not create a new surface in get_surface_portion()";
        return nullptr;
    }
 
    // Blit to dst with BLENDMODE_NONE, then reset src blend mode.
    SDL_BlendMode src_blend;
    SDL_GetSurfaceBlendMode(src, &src_blend);
    SDL_SetSurfaceBlendMode(src, SDL_BLENDMODE_NONE);
    SDL_BlitSurface(src, &area, dst, nullptr);
    SDL_SetSurfaceBlendMode(src, src_blend);
 
    return dst;
}
 
namespace
{
template<typename Range>
bool contains_non_transparent_pixel(const Range& span)
{
    return std::any_of(span.begin(), span.end(),
        [](uint32_t pixel) { return (pixel & SDL_ALPHA_MASK) != 0; });
}
 
/**
 * Calculates the inclusive distance between two array indices.
 *
 * For example, two adjacent columns of pixels should have a
 * distance of two even though their indices are one apart.
 *
 * @pre @a i2 > @a i1
 */
auto cover_distance(int i1, int i2)
{
    return (i2 - i1) + 1;
}
 
} // namespace
 
rect get_non_transparent_portion(const surface& surf)
{
    auto lock = const_surface_lock{surf};
    utils::span pixels = lock.pixel_span();
 
    const auto row_is_not_transparent = [&](std::size_t y) {
        utils::span row_span = pixels.subspan(y * surf->w, surf->w);
        return contains_non_transparent_pixel(row_span);
    };
 
    const auto column_is_not_transparent = [&](std::size_t x) {
        // Striding ahead by width yields all pixels in the x'th column.
        utils::span offset = pixels.subspan(x);
        auto column_span = offset | utils::views::stride(surf->w);
        return contains_non_transparent_pixel(column_span);
    };
 
    rect res;
 
    // Find the first non-transparent row from the top.
    for(int y = 0; y < surf->h; ++y) {
        if(row_is_not_transparent(y)) {
            res.y = y;
            break;
        }
    }
 
    // Find the first non-transparent row from the bottom.
    for(int y = surf->h - 1; y >= res.y; --y) {
        if(row_is_not_transparent(y)) {
            res.h = cover_distance(res.y, y);
            break;
        }
    }
 
    // Discard fully transparent top and bottom rows.
    pixels = pixels.subspan(
        static_cast<std::size_t>(res.y) * surf->w,
        static_cast<std::size_t>(res.h) * surf->w);
 
    // Find the first non-transparent column from the left.
    for(int x = 0; x < surf->w; ++x) {
        if(column_is_not_transparent(x)) {
            res.x = x;
            break;
        }
    }
 
    // Find the first non-transparent column from the right.
    for(int x = surf->w - 1; x >= res.x; --x) {
        if(column_is_not_transparent(x)) {
            res.w = cover_distance(res.x, x);
            break;
        }
    }
 
    return res;
}